1. Field of the Invention
The present invention pertains to low cost moisture resistant and dimensionally stable non-woven continuous webs, and the use of inexpensive furnish for producing such webs.
2. Related Art and Other Considerations
Non-woven continuous web materials have been known in the art at least since the 19th Century, when the English papermaking brothers Sealy and Henry Fourdrinier started their first machine. Over the years many fibers have been used to make various types of webs, including asbestos, bagasse, cotton, glass, hemp, jute, kenaf, sisal, various types of wood cellulose pulp, and many forms of synthetic plastic fibers. For example, U.S. Pat. Nos. 3,773,513 and 3,885,962 to MacClaren teach the use of glass fiber and latex to stabilize a photographic paper.
When health concerns made asbestos fiber obsolete, web makers turned to glass fibers and synthetic fibers made of various plastics. For example, common vinyl floor backing webs which had been made with asbestos fibers were subsequently made of a combination of glass and plastic fibers using a polymer latex as a binder. U.S. Pat. No. 4,274,916 and U.S. Pat. No. 4,373,992 both disclose a dimensionally stable backing web using polypropylene fibers for stabilization. U.S. Pat. No. 4,373,992 further teaches the adding of glass fibers. U.S. Pat. No. 4,269,657 pertains to an asbestos-free web that uses slightly refined virgin cellulose fiber incorporating a low percentage of glass fiber.
The art of xe2x80x9csizingxe2x80x9d non-woven webs is nearly as old as the continuous formation mode. For the purpose of defining xe2x80x9csizing,xe2x80x9d see simultaneously-filed U.S. patent application Ser. No. 09/971,771 and U.S. Provisional Patent application No. 60/238,457 , both entitled xe2x80x9cNON-WOVEN WEB HAVING UNIQUE LIQUID RESISTANCE AND DIMENSIONAL STABILITYxe2x80x9d, which are incorporated herein by reference in their entirety. Products using the materials of the present invention can be either sized, or not sized. The current invention pertains to types of fiber utilized rather than any form of sizing against moisture resistance.
A sampling of prior art directed toward various different types of fibers used in non-woven webs can be found in the following list of U.S. patents, all of which are incorporated herein by reference:
An ordinary 100% cellulose non-woven continuous web material known as xe2x80x9cfeltxe2x80x9d has been used for many years in the production of asphalt saturated roofing felt. This material is used to cover and protect the plywood or composition board comprising the structural part of a sloped roof prior to adding exterior protection. Sloped roof construction is normally used on residential buildings, churches, and schools. The exterior covering over the saturated asphalt felt can be shingles, tiles, slate, or newer materials such as standing ridge steel panels. The layer of asphalt saturated cellulose felt between the structural deck and exterior membrane is often called xe2x80x9cunderlayment.xe2x80x9d
A particular glass fiber reinforced non-woven continuous web material has been used for many years in the production of polyisocyanurate (polyiso) foam board insulation. This rigid plastic foam insulation board has become the most popular type of commercial roofing insulation. It is manufactured by pouring liquid chemical streams on the continuously moving bottom felt, known as the bottom xe2x80x9cFacer,xe2x80x9d with a second Facer being placed on top of the foaming streams. The polyiso foaming liquid is deposited between two webs of the Facer felt, cured into a unified foamed board, and then cut into insulation board lengths. The largest producer of this facer felt, Atlas Roofing Corporation, developed a glass fiber-utilizing facer which Atlas refers to as xe2x80x9cGlass Reinforced Feltxe2x80x9d (GRF) Facer. Certain aspects of this facer product are disclosed in U.S. patent application, Ser. No. 09/425,051, which is incorporated herein by reference in its entirety. The GRF Facer has a higher degree of dimensional stability than 100% cellulose felt. As an integral part of an insulation board, GRF Facer adds strength and durability to a lightweight insulation board that is used in a severe environment. Strength and durability are important because commercial roofing products suffer some of the most intense punishment experienced by building construction products.
Historically, asphalt saturated roofing felt and GRF Facers have primarily used recycled waste paper as the raw material source for fiber. In most cases, OCC (Old Corrugated Container) is the main source of fiber. OCC is normally the highest cost material used in a paper mill that uses nothing but recycled waste paper. Mixed waste, or office waste, or newsprint, or wood flour, or some mixture of these has been the lower cost fiber source to augment the OCC. The successful use of recycled glass fiber has improved the properties of the facer web while keeping the cost reasonable. The cost of either virgin glass fiber or virgin cellulose fiber is much too high for this facer.
For the purpose of describing this invention, the term xe2x80x9cClarifier Sludgexe2x80x9d refers to the rejected solids that are separated from the post-processing water by the cleaning and recycling systems in paper and pulp mills. Thus, xe2x80x9cClarifier Sludgexe2x80x9d encompasses but is not limited to the mixture of short fibers, extremely large fibers, and inorganic contaminates that are separated from the recycling water of a pulp and/or paper mill. Clarifer Sludge is sometimes sent to an approved landfill. Most of it is burned as boiler fuel after some water has been removed. Several solid/liquid separation systems in use have trade names, but herein they are collectively and generically called xe2x80x9cclarifiers.xe2x80x9d Both pulp mills and paper mills have a need to clean their post-processing water, especially if it is an effluent going back into the public sewer or watershed systems. Untreated Clarifier Sludge is notoriously unacceptable as a paper mill furnish.
Thus, the owner of the pulp and/or paper mills primarily direct their efforts to the clarification of the water, rather than emphasizing the collection of solids (e.g., Clarifier Sludge). The collection of solids is an onerous but necessary part of the cleaning of pulp and paper mill effluent water. Disposal of Clarifier Sludge is often hampered by environmental concerns. The quality of the fiber found in this recovered solids mass will depend upon the source of the fiber used by the paper mill. If a pulp mill is integrated with a paper mill, these recycling water streams are usually mixed prior to clarifier treatment. In this case, the fiber quality of these mixed streams will be higher than most any other situation. The reason is that some of this fiber has never been through a refiner. Even the relatively high quality Clarifier Sludge from a de-inking plant will have no unrefined fibers. The highest quality sludge is found where a pulp mill treats their own recycling water, separate from a paper mill.
Many attempts have been made at improving wet Clarifier Sludge to a state of being useful. At least by the mid-1970s a company developed a system for recovery of fiber from paper mill effluent. U.S. Pat. No. 3,833,468 to Boniface teaches such a system. Other U.S. patents concentrating on either the apparatus to improve, or the method of improving, waste Clarifier Sludge include the following:
The various processes to improve quality of Clarifier Sludge are relatively expensive, raising the cost of acceptable fiber furnish. In some instances, the freight costs to transport this type of reclaimed fiber are prohibitive. Excessive freight costs can be due to the large percentage of water usually found in this material, or the distance from the source to the paper mill using the material, or both.
The quality of untreated Clarifier Sludge has been so low that it has not been considered suitable as a substitute for waste paper. Only after being treated by one or more of the various schemes noted above has it been useful. One example, U.S. Pat. No. 5,423,993, teaches a method using a fiber recovery system inside a paper mill. It appears that no paper mill has heretofore successfully used untreated Clarifier Sludge.
The quality of waste paper is lower now than at any time in the past, primarily due to more recycling. Some experts estimate that any given Kraft fiber originally used in a cardboard box can be reused at least five different times in five different waste paper mills. Another major reason waste paper quality has dropped is that the suppliers allow more contamination from metals and plastics. A further problem is the large increase in coated papers being recycled. Coated paper means high levels of mineral pigments as ash. Wide fluctuations in the amount of coated paper in xe2x80x9cMixed Wastexe2x80x9d causes a loss of control over the percent ash in felt. The lack of consistent properties causes endless problems for a paper mill using 100% recycled waste paper. Any given truckload of any grade of waste paper will contain significantly different materials than any other truckload of the supposedly same grade. In today""s market, it is virtually impossible to purchase consistent properties in any grade of waste paper. This makes it difficult to manufacture a web of felt, with or without glass fibers, with uniform properties.
Thus, there remains a need for a more consistent source of secondary cellulose fibers to make dry felt both for asphalt saturated underlayment and for facers (e.g., glass reinforced felt facers) for polyiso foam boards. Therefore it is an object of the present invention to provide an economical dry felt having more consistent properties by utilizing a more uniform source of cellulose fiber.
The non-woven web of the present invention is comprised of recycled cellulose fiber and untreated Clarifier Sludge, and optionally, recycled glass fiber. Unlike uses of reclaimed Clarifier Sludge whereby the material has been treated in some fashion to improve its quality, the non-woven web of the present invention utilizes untreated Clarifier Sludge.
The Clarifier Sludge used in the present invention is dry enough to handle, e.g., with a front-loader, and in one example varies between about 30% and about 45% solids. The Clarifier Sludge can be added to web-forming equipment (e.g., papermaking equipment) either in a waste paper disintegrator or into a recycling apparatus (e.g., broke pulper) whose output is metered into a refiner tank of the web-forming equipment. In an embodiment utilizing a broke pulper for introduction of the Clarifier Sludge, a broke pulper is filled with Clarifier Sludge and water to a consistency of about 3.5% solids. In a practical example, over fifty percent (50%) of the total paper making furnish (i.e., paper making solids) is Clarifier Sludge.
The use of the Clarifier Sludge of the present invention for papermaking involves selection of proper retention and drainage agents. In particular, the retention and drainage agents must enable solids (e.g., the impurities) of the Clarifier Sludge to stay in a sheet formed in the papermaking machine and still permit good liquid drainage. Proper agent selection enables a bundling of the short fibers and the impurities of the Clarifier Sludge with the longer fibers in the wastepaper, and at the same time permits quick liquid drainage between the forming bundles; e.g., xe2x80x9cpin-flocsxe2x80x9d.